Tokkai Hei 10-267117 published by the Japanese Patent Office on Mar. 24, 1997, discloses an infinite speed ratio continuously variable transmission (hereinafter referred to as IVT) which varies a speed ratio infinitely by combining a fixed speed ratio transmission and planetary gear mechanism with a continuously variable transmission.
The IVT is provided with two clutches, i.e. a power recirculation mode clutch and a direct mode clutch. The direct clutch is provided between the output shaft of the continuously variable transmission (hereinafter referred to as CVT) and a ring gear of the planetary gear mechanism. The ring gear is connected to an unit output shaft. The power recirculation mode clutch is provided between an output gear of the fixed speed ratio transmission and a carrier of the planetary gear mechanism.
The IVT is operated in a direct mode wherein the direct mode clutch is engaged and the power recirculation mode clutch is disengaged, or in a power recirculation mode wherein the direct mode clutch is disengaged and the power recirculation mode clutch is engaged. The change-over of the above two modes is performed at a rotation synchronous point (RSP) where the speed ratio of the CVT takes a specific value.
When the mode change-over is performed, in order to prevent a change-over shock due to engaging/disengaging of the clutches from occurring, engaging of a clutch is performed slowly via a half-engaged state. A considerable time period is therefore required from the start of the mode change-over until it is completed.
During the mode change-over, the speed ratio of the IVT (referred to hereafter as IVT ratio) must be fixed at the rotation synchronous point RSP, but due to the variations of the vehicle running state, the IVT ratio may deviate from the rotation synchronous point RSP and it also causes a shock in the course of the clutch engagement.
It is therefore an object of this invention to enable a rapid mode change-over of the IVT while preventing the change-over shock from occurring.
In order to the above object, this invention provides an infinite speed ratio continuously variable transmission, comprising: an unit input shaft; a continuously variable transmission which transmits a rotation of the unit input shaft to a first output shaft at an arbitrary speed ratio; a fixed speed ratio transmission which transmits the rotation of the unit input shaft to a second output shaft at a fixed speed ratio, a direct mode clutch; a power recirculation mode clutch, one of the direct clutch and the power recirculation mode clutch comprising an electromagnetic two-way clutch that, when energized, transmits a drive force in a first direction and in a second direction opposite to the first direction, and when changed from the energized state to the non-energized state, transmits the drive force only in the direction of a drive force transmission at the change-over to non-excitation, and when the direction of the drive force transmission changes to an opposite direction, disengages; and a planetary gear set comprising a first rotation element joined to the first output shaft via the direct mode clutch, a second rotation element joined to the second output shaft via the power recirculation mode clutch, and a third rotation element which varies a rotation direction and a rotation speed according to a difference between a rotation speed of the first rotation element and a rotation speed of the second rotation element.